This invention relates to a method for removing sulfur compounds from fluid streams. More particularly, it relates to a method for removing sulfur compounds including sulfur dioxide (SO.sub.2) from fluids.
Removal of such sulfur compounds as sulfur dioxide, e.g. from fluids such as industrial and utility gas emissions, is increasingly important. Acid rain is believed to occur when sulfur dioxide in such emissions undergoes chemical changes in the atmosphere and returns to earth with precipitation.
There are numerous techniques for removing sulfur compounds from fluid streams containing them. One common process employs limestone scrubbing. The disadvantage of this process is the necessity of disposing of the large volume of solid waste produced. The wastes are not generally recycled. Another system, taught in U.S. Pat. No. 4,366,134, employs potassium or sodium citrate to selectively remove SO.sub.2 from a gas stream. While the wastes from this process can be recycled, recycle is expensive because thermally stable salts are formed and require higher heat for regeneration.
More recent patents teach the use of certain piperazinone derivatives. For instance. U.S. Pat. No. 4,112,049 teaches use of certain piperazinones and N,N'-alkyl piperazinone. In another patent, U.S. Pat. No. 4,530,704, the removal of SO.sub.2 from a gas stream is accomplished by contacting a gas stream containing it with an aqueous solution of a piperazinone, morpholinone or N-alkyl substituted derivatives thereof, e.g. N,N'-dimethyl-2-piperazinone. In U.S. Pat. No. 4,783,327 certain hydroxyalkyl substituted piperazinones are taught for use in a similar manner.
Tons such as those formed on admixture of sulfur compounds such as sulfur dioxide with water are known to be removed from fluids such as water by means such as membranes to separate an absorbing solution from a solution having the ions to be removed. For instance, Wisniewska et al., disclose in Desalination 56 (1985) pp. 161-173, Amsterdam removal of nitrate from a first solution into a second solution on the opposite side of a membrane from the membrane. Similarly, RAI Research Corporation in Product & Data Guide, Raipore Membranes, N.Y. discloses the use of membranes having a solution of potassium hydroxide (an absorbent) on one side to remove sulfate, nitrate and cyanide anions from a solution thereof on the other side of the membrane.
It would be advantageous to have a process for removal of sulfur compounds such as sulfur dioxide which employs an aqueous solution and uses an absorbent which has a high capacity for absorbing sulfur dioxide. The absorbent would desirably be regenerable. It is also desirable that this absorbent has adequate water compatibility at ambient or higher temperatures and its salts are water soluble to avoid inducing scaling or plugging of plant equipment.